Field of the Disclosure
Embodiments disclosed herein relate generally to vibratory separator components for collecting wellbore strengthening materials. More specifically, embodiments disclosed herein relate to removable vibratory separator components for collecting wellbore strengthening materials during drilling. More specifically still, embodiments disclosed herein relate to removable vibratory separator components for collecting wellbore strengthening materials on offshore drilling operations.
Background Art
Oilfield drilling fluid, often called “mud,” serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. Typically, the mud is mixed at the surface and pumped downhole at high pressure to the drill bit through a bore of the drillstring. Once the mud reaches the drill bit, it exits through various nozzles and ports where it lubricates and cools the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drillstring and the drilled wellbore.
Furthermore, drilling mud provides a column of hydrostatic pressure, or head, to prevent “blow out” of the well being drilled. This hydrostatic pressure offsets formation pressures thereby preventing fluids from blowing out if pressurized deposits in the formation are breached. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) itself and the density (or its inverse, specific gravity) of the fluid used. Depending on the type and construction of the formation to be drilled, various weighting and lubrication agents are mixed into the drilling mud to obtain the right mixture. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Generally, increasing the amount of weighting agent solute dissolved in the mud base will create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blow outs, and drilling mud that is too heavy may over invade the formation. Therefore, much time and consideration is spent to ensure the mud mixture is optimal. Because the mud evaluation and mixture process is time consuming and expensive, drillers and service companies prefer to reclaim the returned drilling mud and recycle it for continued use.
Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit at the bottom of the borehole to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling fluid exiting the nozzles at the bit acts to stir-up and carry the solid particles of rock and formation to the surface within the annulus between the drillstring and the borehole. Therefore, the fluid exiting the borehole from the annulus is a slurry of formation cuttings in drilling mud. Before the mud can be recycled and re-pumped down through nozzles of the drill bit, the cutting particulates must be removed.
Apparatus in use today to remove cuttings and other solid particulates from drilling fluid are commonly referred to in the industry as “shale shakers.” A shale shaker, also known as a vibratory separator, is a vibrating sieve-like table upon which returning solids laden drilling fluid is deposited and through which clean drilling fluid emerges. The shale shaker may be angled table with a generally perforated filter screen bottom. Returning drilling fluid is deposited at the feed end of the shale shaker. As the drilling fluid travels down length of the vibrating table, the fluid falls through the perforations to a reservoir below leaving the solid particulate material behind. The vibrating action of the shale shaker table conveys solid particles left behind until they fall off the discharge end of the shaker table. The above-described apparatus is illustrative of one type of shale shaker known to those of ordinary skill in the art. In alternate shale shakers, the top edge of the shaker may be relatively closer to the ground than the lower end. In such shale shakers, the angle of inclination may require the movement of particulates in a generally upward direction. In still other shale shakers, the table may not be angled, thus the vibrating action of the shaker alone may enable particle/fluid separation. Regardless, table inclination and/or design variations of existing shale shakers should not be considered a limitation of the present disclosure.
Recently, drilling fluids containing bridging materials, also known in the art as wellbore strengthening materials or loss prevention materials, have seen increased use in drilling operations where natural fractures in the wellbore allow drilling fluid to escape from the circulating system. Wellbore strengthening materials are typically mixed into the drilling fluid and used to bridge the fractures to prevent fluid loss into the formation. Such wellbore strengthening materials are also used in stress cage drilling, which involves intentionally creating fractures in the wellbore and bridging the fractures with the materials. Such applications create a hoop stress and stabilize the formation.
Wellbore strengthening materials typically are more expensive than other additives used in drilling fluid components. Thus, drillers benefit when wellbore strengthening materials are recovered during waste remediation. However, during drilling waste remediation, which may include use of vibratory separators to remove cuttings from return drilling fluid, as the cuttings are removed, the wellbore strengthening materials are also removed. The removal of wellbore strengthening materials during drilling waste remediation requires additional wellbore strengthening materials being added to the drilling fluid, thereby increasing the cost of the drilling operation.
Accordingly, there exists a need for methods and apparatuses to recover wellbore strengthening materials during separation operations at drilling locations.